It can be considered that a process of detecting multiple targets from among display of multiple items is composed of some sub-processes, namely, sensory reception, identification of items in display, and scanning of contents in the memory. The purpose of this study was to investigate the modes of the sub-process from the point of view of serial and parallel processing. We compared performance in sigle-target and multiple-target detection tasks in order to investigate whether or not multiple targets can be detected simultaneously.Experiment 1 tested modes of the sensory reception and the identification for letter-targets. The results suggested serial searching pocess in the sensory reception, and parallel searching process in the identification.Experiment 2 tested the modes of identification for color-targets. Reaction time incresed lineally as the number of color stimulus incresed. The result indecats that serial searching process proceeds in the identification of color.Experiment 3 tested the searching process of letters in display and scanning process in memory. It became clear that serial process proceeds in searching letters and scanning of memory. It was also found that serial process acts in either case of OR-task, AND-task, and OR-AND task.In Experiment 4, the searching process of colors in display and scanning process of memory were tested. The results were that serial process acts in scanning of memory, and parallel process in detection of color.